The present invention relates to audio amplifier units which output audio signals of rear loudspeakers to channels of front loudspeakers.
Among various recent audio (video) sources, such as DVD Video disks (DVDs), are ones having recorded thereon 5.1-channel or other type of multi-channel audio signals with a view to enhancing a feeling of presence or realism. For example, audio amplifiers and loudspeakers of six channels are normally required for reproduction of 5.1-channel audio signals.
Also, in recent years, it is getting more and more popular to reproduce AV (AudioVisual) software, such as software recorded on a DVD, via a personal computer. In such cases, the multi-channel audio signals are usually reproduced through a pair of left (L) and right (R) channels, because the personal computer is rarely connected to a multi-channel audio system capable of appropriately reproducing 5.1-channel audio signals. However, thus reproducing the multi-channel audio signals by only the two channels can not reproduce a feeling of presence or realism to a satisfactory degree.
Further, there has been proposed a technique which outputs audio signals of rear (surround) channels via front loudspeakers, i.e. front L- and R-channel loudspeakers after performing a filter process on the audio signals of the rear channels to allow their sound images to be localized at virtual rear loudspeaker positions. But, the proposed technique would present the inconvenience that it can not achieve accurate sound image localization because filter coefficients and other parameters employed are fixed.
Namely, although sound image localization perceived by a human listener depends greatly on head-related transfer functions that represent audio-signal transfer characteristics determined by a shape of the head of a human listener, the conventional apparatus for simulating multi-channel audios are generally arranged to only simulate head-related transfer functions of a predetermined head shape; namely, they never allow for different head shapes of various human listeners.